1) 3/13 + 4/13 = 7/12) 13/28 - 1/7 = (131 - 281) / 287 = (13 - 28) / 196 = -15 / 196 = -15/193) 13 - 1/7 = 13 - 1/7 = (137 - 1*7) / 7 = 91 - 1 / 7 = 90 / 7 = 12 6/7.
1) 3/13 + 4/13 = 7/1
2) 13/28 - 1/7 = (131 - 281) / 287 = (13 - 28) / 196 = -15 / 196 = -15/19
3) 13 - 1/7 = 13 - 1/7 = (137 - 1*7) / 7 = 91 - 1 / 7 = 90 / 7 = 12 6/7.